When you are trying to improve SEO, what search engines do you look at? Personally I only checkup on Google because that is the primary one and is used by most people, indexing is also generally easier as well.
Usually everyone will focus on Google because its the most popular search engine 😀 And, I think webmasters have a special affinity to Google because Gbot visits your site everytime irrespective of your stats 😀
I focus on Google and Bing. By doing Bing, it automatically extends to Yahoo as well if I remember correctly. I have also done a little work with Baidu, but it was limited to just making sure that everything was submitted to it.
I use google only to search and never find people asking/discuss other search engines. I submitted to three most popular sites when I first created a forum...google, bing and yahoo
Bing and Yahoo would require the most focus cause there at least a forum has a chance. Google is very difficult to rank in. However, there still should be an effort, though.